Process of chemical nickel plating



Nov. 10, 1953 FK'TALJflE\' ET'AL PROCESS OF CHEMICAL NICKEL PLATING Filed April 21, 1951 HVVENTDRS Paul Ta/mey BY William J Cr'ehan Patented Nov. 10, 1953 UNITED STATES H PATENT. OFFICE assasaa' I Y Hinsdale, 111., assignors to General American Transportation Corporation, Chicago, 111., a

corporation of New York and William J. Crehan,

Application April 21, 1951, Serial No. 222,222

11 Claims. (Cl. 117-102) The present invention relates to processes of chemical nickel plating and more particularly to an improved method of utilizing the'.bath solutions of nickel plating processes jsuchas those disclosed in the copending applications of Gregoire Gutzeit and Abraham 'Krieg, Serial No. 194,656, filed November 8, 1950, and of Gregoire Gutzeit and Ernest J. Ramirez, Serial No. 204,424, filed January 4, 1951 and in United States Letters Patent No. 2,532,283, issued to Abner Brenner and Grace E. Riddell on December 5, 1950.

In the Brenner and Riddell patent .there is disclosed a batch process for chemically plating with nickel by the use of a plating bathincluding nickel ions and hypophosphite ions, the concentration of the bath being maintained at a predetermined value .by the addition of the reagents of the bath at .regular intervals.

In the Gutzeit and'Krieg application, there is disclosed a batch process of chemically plating a catalytic material, such as steel, with nickel, by contacting the material with an acid bath containing nickel ions and hypophosphite ions and a buffer. This process is carried on under certain optimum conditions which are as follows: The ratio between nickel ions and hypophosphite ions in the bath, expressed in molar concentrations, is within the range 0.25 to 0.60; the absolute concentration of hypophosphite ions inv the bath, expressed in mole/liter, is within the range 0.15 to 0.35; the absolute concentration of the buffer in the bath is approximately equivalent to two carboxyl groups for every nickel ion that can be deposited, for instance, in the case of sodium acetate, 0.120 mole/liter of acetate ion'; the initial pH of the bath is within the approximate range 4.5 to 5.6; the temperature of the bath is slightly below the boiling point thereof, about 99 Centigrade; and the ratio between the volume of the bath, expressed in cmfi, and the surface area of the material that is to be plated, expressed in cm. V/A, is not greater than 10. The bufiers mentioned in this application and employed in the test therein referred to are soluble acetates, such as sodium acetate.

In the Gutzeit and Ramirez application, there is disclosed a batch process of chemically plating a catalytic material, such ,as steel, with nickel, by contacting the material with a bath containing nickel ions and hypophosphite ions "and an exaltant in the form of a simple short chain saturated aliphatic dicarboxylic acid. This process is also carried on under certain optimum conditions: The ratio betweennickel ions and hypophosphite ions .in the bath, expressedin molar concentrations, is within the range 0.25 to 1.60; the absolute concentration of hypophosphite ions in the bath, expressed in mole/liter, is within the range 0.15 to 1.20; the absolute concentration of the exaltant in the bath is approximately equivalent to two carboxyl groups for every nickel ion that can be deposited, for instance, in the case of sodium succinate, at least 0.05 mole/liter of .succinate ion; the initial pH of the bath is within the"approximate range 4.3 to 6.8; the temperature of the bath is slightly below the boiling point thereof, about 99 C. at atmospheric pressure; and the ratio between the volume of the bath, expressed in cmfi, and the surface area of the material that is to be plated, expressed in cm. V/A, is not greater than 10. The exaltants mentioned in this application and employed in the test therein referred to are soluble salts. of malonic, succinic, glutaric, and adipic acids.

In these copending applications, it was pointed out that the plating reaction involved, represented, for instance, by the equation:

( cat. 2Na(HqPO2) 21320 NlClz f sur.

ing power ofthe hypophosphite ion is impaired at low pH values and the dissolution rate of the nickel coating or plating in the strongly acid bath will approach and eventually equal the rate of deposition of the nickel.

Moreover, it was pointed out that in order to obtain high nickel plating rates, these processes must be carried out within the optimum pH ranges of the specific baths, and that in order to retard or prevent the formation of black pre cipitate in the baths, the ratio between the volume of the bath, expressed in cmfi, and the surface area of the catalytic material that is to be plated, expressed in cm. V/A, should be kept below 10. v

I On the other hand, in any batch or static system without regeneration, there is a limit to the thickness of the nickelcoat whichmay beplated 3 Further, the rate of plating decreases as the bath is exhausted, with the consequence that a much longer time is required to obtain an equal increment of thickness near the end of the process than in the beginning. Practically speaking, the ultimate thickness obtainable in a batch or static process is in the range of 0.0005 inch to "0.0010 inch in a period of two hours. The regeneration of the plating bath is unsatisfactory because it has been found that regeneration of a batch bath produces a laminar structure in the coating. n

Thus it is of great practical value to be able to deposit any desired thickness of nickel, while the concentrations of the reagents are kept within the optimum ranges mentioned in order to achieve the best quality of plating and the highest plating rate. Insofar as the maintenance of a substantially constant pH is concerned, periodicor continuous addition of a soluble alkali hydroxide or a soluble alkaline salt provides a means of achieving this objective; and, also, this result may be attained by the addition of a buffer salt or a combination of buffers, i. a, compounds comprising the anion of a weakly dis- ;sociated acid and a cation able to form a stron base,

The present invention involves improved process steps for maintaining substantially constant the relative and optimum concentrations and proportions of the reagents in the bath, as well as the holding of the pH of the bath within any desired narrow optimum limits, while permitting the plating of any desired thickness of a continuous and homogeneous coating of nickel on the surface area of a catalytic material in-a simple and efiicient manner. In carrying out the process of the present invention, it may be observed that if the volume of the bath were infinite, while the surface area of the catalytic material to be plated was small, the pH value of the bath would not change, provided 'suflici'ent agitation is supplied to avoidany local variation. In other words, if a small object to be plated is placed in Ta relatively large. volume of well agitated bath, the drop in pH due to the plating reaction is so minute as to be practically without effect. On theot'her hand, it has'been found that in a static (as opposed to a dynamic) system, excessive "agitation of the bath decreases both the plating rate and the quality of the plating, and that a large ratio of the bath volume to the catalytic material surface area (V/A), tends to favor the formation of black precipitate. Further, and of great importance, a relatively high temperature of the bath tends to favor the formation of black precipitate even in the ab- 'sence of a catalyst, by spontaneous thermal decomposition. In order to obtain, in addition to other things, the advantage of a large volume of available bath without encountering the disadvantage of a V/A ratio outside of the optimum range, the plating operation proper, according to the present invention, is carried out in a rela- "tively small insulated and heated. plating chamber, through which the bath, first preheated to the proper temperature, flows at a relatively low rate, a much larger proportion of the bath being stored in a relatively large reservoir at a substantially lower temperature at which the rate of thermal decomposition is low, for example,

substantially at room temperature or even higher. The overflow from the plating chamber is returned directly to the reservoir for re-use;

and when the's'olution in the reservoir is partly exhausted, it may be regenerated by the periodic or continuous addition of the contained reagents.

It is therefore the primary object of the present invention to provide an improved chemical nickel plating process of the character described in which the plating reaction involved is carried out continuously in a dynamic system and more efficiently and more nearly uniform than theretofore, thereby rendering the process more desi'rable from a commercial standpoint.

Another object 'of the invention is to provide an improved process of the character indicated "that is continuous so that a substantially uniform "and homogeneous nickel coating of any desired thickness may be deposited upon the surface area of a catalytic material that is to be plated.

A further object of the invention is to provide it improved process of the character indicated employing a given nickel plating bath, wherein the bulk of the bath as a substantially inactive solution is stored in a reservoir at a temperature substantially lower than that of the bath in the plating chamber, a small portion of the solution as a plating bath is held at an elevated temperature in a plating chamber, and the solution is circulated at a low rate from the reservoir to the plating chamber and then back to the reservoir, whereby random chemical reduction of the nickel ions in the bath and the consequent formation of black precipitate is eliminated or greatly minimized.

These and other objects and advantages of the present invention will be understood from the "foregoing and following description taken with the accompanying drawing, in which Figure 1 is a schematic diagram of an arrangement of ap*- paratus for carryingout the process of the present invention.

Referring now to Fig. l, the dynamic system there illustrated comprises a reservoir l0 containing a large volume of the solution II and a plating chamber 1'2 containing a small volume of the bath l3, the lower portion of the reservoir HI being connected to the lower portion or the plating chamber 12 by a conduit l4. A valve i5 is arranged in the "conduit 14 'so as to accommodate regulation of the rate of 'fi0W of the solution H from the reservoir 10 in the bath '13 in the plating chamber 12. The upper portion of the solution H in the reservoir [0 is disposed at a "suitable jele'vation above the upper portion of the bath l3 in the plating chamber "12,wh'ereby the flow or the solution H through the conduit M takes place by the action of gravity, the bath -l3 in the plating chamber I2 ibein'g overfiowed from the upper portion thereof into'a surrounding launder [6 that communicates via a conduit H with a variable speed liquid :pump I8. The pump 18 normally returns the 'o'verflowed bath 13 via a conduit [9 to the upper portion of the solution H in the reservoir 10; and the conduit 19 is also connected via a nornially closed valve '20 to a draw-01f conduit 2|. The intermediate portion of the conduit [4 is provided with a serpentine section Ma that is enclosed by a jacket '22; and the wall of the plating chamber 2 isprovided with a surround- 'ing jacket 23. The jackets 22 and 23 are .arranged in communicating relation; steam'is supplied via a pipe 24 into the heating chambers defined by the jackets 22 and 23; and condensate ?is removed from these heating chambers via a pipe 25. Thus the solution H in theserpentine '75 section Ila of the conduit [4 preheated to the temperature required by any particular plating bath prior to the introduction thereof into the plating chamber 12; andthe bath l3 contained in the plating chamber I2 is heated to maintain the temperature noted.

A heat exchanging device is shown at 28 which is utilized to reduce the temperature of the bath before it is reintroduced into the storagechamber H. In small systems this. cooling device may be eliminated as the natural cooling effect of the parts I], I8, 19 and I0 may ,sulfice.

The catalytic material that is to be plated with the nickel is immersed in the bath l3 in the plating chamber l2, and is withdrawn therefrom after a time interval corresponding to the thickness or weight of the nickel coating or plating thereon that is desired. Finally, the reservoir I0 is provided with a drain pipe 26 that is normally closed by an associated valve 21; and of course the component elements of the apparatus or system are formed of noncatalytic materials such as glass, quartz, certain synthetic resins, etc., to prevent the plating of nickel thereon. Thus the major differences between the solution I l in the reservoir and the bath IS in the plating chamber are temperature, the presence of a catalytic material, volume and chemical composition. The average chemical composition of the bath l3 and the solution ll arediflerent to the extent that nickel has been removed and hypophosphite oxidized to the products of its reaction. These diiferences in composition, however, are by no means as marked as the differences in a batch plating bath between the initiation and conclusion of the plating cycle. The resultant advantages have heretofore been described.

In carrying out any of these processes, the materials that may be coated orplated with nickel include for example such common materials as iron, cobalt, nickel and palladium. Some materials, not catalytic by themselves, can be plated by the useof iron as an initiator. For instance, copper can be used as a basis material, by contacting it with an iron wire to initiate the plating reaction, after which the wire is removed. It should, therefore, be understood that whenever we refer to a catalytic material,

we mean thereby a basis material that is catalytic by itself or one that is made catalytic by association with another material. The following elements are examples of noncatalytic materials which ordinarily may not be nickel plated: bismuth, cadmium, tin and lead. Prior to immersing a specimen of catalytic or other basis material to be nickel plated in the bath contained in the plating chamber, the specimen should be first mechanically cleaned to remove any oxide and mill scale; also, the specimen should be degreased and then lightly pickled in a suitable acid, such as HCl.

In carrying out the process of the present invention, employing the apparatus illustrated, and to demonstrate that under these conditions no buifer is needed to produce a good nickel plating, the following tests were performed: baths of the character of that disclosed in the Gutzeit and Krieg application were employed that contained only nickel ions, hypophosphite ions and sodium ions, nickel hydroxide being dissolved in hypophosphorous acid to produce nickel hypophosphite, and sodium hypophosphite being added to obtain the proper concentrations. The pH of the baths were about 3.0 as prepared, and were then adjusted with sodium hydroxide to the optimum 6. values of 4.5.to.4.6. These baths thus prepared and having the specific compositions noted were employed in the plating of steel samples with the following results:

Table I Tests No. 1

Bath composition by analysis:

Nimole/liter (HQP Oz) mole/literpH adjusted to Test conditions:

bath, liters. Volume of plating chamber, cm. Area of steel sample cm. V/A Average rate of 5.88 5.88 5.88.

From Table I, it may be seen that the rate of nickel plating expressed in gm./cm. /min. is low, but fairly constant, regardless of the rate of flow of the bath and regardless of the length of time of the plating operation.

Much higher rates of nickel plating can be achieved in accordance with the process of the present invention by using a buffer as indicated in the Gutzeit and Krieg application or by employing a bath of the character of that disclosed in the Gutzeit and Ramirez application. For example, using the latter type bath a rate of nickel deposition of 4.'75 l0' gms./cm. /min. was achieved.

A very important advantage of the dynamic system of the present process over the batch techniques of the processes of the prior applications and the patent mentioned resides in the circumstance that the chemical composition of the actual plating bath changes very slowly. This results in (1) a very homogeneous composition of the coating which effects a better control of the physical and chemical properties thereof, and (2) a substantially faster plating.

This first result flows from the fact that if any additions are needed to make up for exhaustion of certain reagents, such additions are made in the reservoir thus insuring the constancy of the bath in the plating chamber as will be shown below. The second advantage follows from the first. Because of the constancy of the plating bath in the plating chamber, there is no dilution to any appreciable extent of the amount of nickel to be reduced or of the hypophosphite which does the reducing, thereby eliminating any slowing down of the reaction. Thusthe over-all'rate of plating is higher. .Actually, we have found the rate increase to be even more substantial than could be expected to result from the constancy of the plating. solution. It is believed that the laminar flow which helps to remove the hydrogen bubbles has a decided effect in speeding up the rate.

' Thefollowing tests were carried out in accordance with the process of the present. invention employing baths of the character set forth in the Gutzeit and Ramirez application wherein the eases periodically ages Table I1 U Cy cl Cycle .Gycl Cycle Tests No. I No. a 1 No. No.

Bath composition byanalysis:

Ni mole/liter 0,09 0.09 0.09 0.09 Hirosmolelliter- 0; 225' 0.225 l) 225 0.225 (Cd-1 00* mole/liter 0.06 0106 0.60 0. 06 pH adjusted to 4'. 48' 4. 61 4150' 4. 50 Test Conditions:

Total volume'oi bath; liters- 2' 2 2 2 Volume of plating chamber,

c114 65. 65 65 65 Xre'a'oi' steel sample; cm 39 39 39 39 V/A 1. 7 1. 7 1.7 1. 7 Average rate of flow, cm /min. 49 62 28 t 34 Duration'ofte'st, mih's'. 41' 32 37 29 97 97 97 97 ts Weight of plating, gm 0. 7499 0. 6760 0. 8405 0. 5350 Rate of plating R X gms/ cmfi/ min 4 369 5.41 5.8 4. 73 Einbl'pH 1 4. 22 4; 36 u 4. 35 Appearance (l Analysis of platin Percent Ni 95. 9 94. 1 92. 3 94. 3 Percent P 7.4 1 6 .97 7.6% 8.9

1 Bright andsmooth.

From Table II it will-be observed that the specific composition of the nickel-phosphorous coatings through cycle '7 varies only slightly. (Due to the small quantity of coated material relative to basis material, this type of analysis is subject to some variation. The ranges and values given are consideredwithin the analytical error.) Further it is specifically pointed out that thiscontinuous and homogeneous plating produced by the dynamic system of the present invention" is entirely different in character from a composite plating that is sequentially built up employinga plurality of batch plating operations ofthegeneral character disclosed in the Gutzeit and Kriegapplication and in the Gutzeit and Ramirez application. It is postulated that this difference resides in the circumstance that when a series of batch plating operations are employed to-obtain a relatively thick composite coating, a series of layers of coating are really obtained. In-any case, the layers of coating exhibit a stratified characteristic, whereby the coating is not homogenous and uniform throughout either with; respect to specific chemical composition-in regfard to nickel and phosphorous or with respect to hardness and other physical properties. When; the article to be plated remains in the bath but periodic additions are madeto the plating bathas in Brenner andRiddell, thereis an entirely different laminar structure than when employing themethod of the'present invention.

Moreover, it is noted that the dynamic'system of'the present'inv'ention accommodates the contiriuous plating of' mrge weights or" thick coat ings of nickel as compared with the prior batch plating operations. This circumstance is aptly demonstrated by the following test in which there was employed a bathjof the generaichara'cter of that set forth in Gutzeit and Ramirez. This bath thus prepared and having the specific composition noted wasperiodically "regenerated by additions of 'NiClz and Na.(H2PO2) to thereser-f ion and was" emerges in the plating of'a steel sam iewiththemncwme results?" Table III hath composition by theses:

Test'Conditions': V r Total-volume of bath, liters 12. Volu'r'ne of plating chamber,

ciI-ically observed that over 12 grams of nickel were deposited in this test to form a coating on the steel sample having a thickness of 5 mils. Moreover,- there is no critical limitation to the ultimate thickness of the nickel coating that maybe deposited, since the solution in the reservoir may bereadily periodically or continuously regenerated in the manner previously explained to'prese'rve both the concentrations and proportions of the reagents thereof and also to hold the desired pH thereof, whereby the efiiciency of the bath in the plating chamber is constant.

In order to demonstrate that equivalent ru'f Sult's may be readily obtained employing samples foirhedof basis materials',other than steel, a test was conducted employing a bath of the general character" Ofth at' set iorth in the G utzeit and Ramirez application, Wherein the bath was em:

ployed'in the plating of copper tubing, with the followingresults. p

Table IV Basematerial l l Copper tubing. Activation (catalyst) l Iron.

Bath eomposiuon'by analysis:

Test conditions? v Total vol. o f-bath, liters; r 5.; vol; of plating chamber, cm. 65'.

The" dynamic syste mof the present invention has also been testedwiththe use of the Brenner patentwith the following results:

the elevated temperature Approximate time 110 minutes. Volume of solution in reservoir 780 cc. Volume of plating bath 50 cc.

Area of steel plated 20 cm. Average flow per minute 6 cc./min. Temperature 97 C. Initial pH 5.05.

Final pI-I 4.3.

Weight gain 0.7483 gm. Rate -R 10 gms./cm. /min 3.4. Appearance Slightly rough.

From the foregoing,it is apparent that great advantages are obtained by the process of the present invention employing the dynamic system in chemical nickel plating of catalytic materials utilizing baths of the general composition set forth in the Brenner and Riddell patent mentioned and in the prior applications of Gutzeit and Krieg and of Gutzeit and Ramirez, or any other chemical nickel plating bath of the same type, particularly with reference to the homogeneous character of the nickel-phosphorous deposits concerning the physical" and chemical characteristics thereof and to a greatly increased rate of plating, as wel1 as thickness. Moreover, the dynamic system permits the utilization of a large effective volume of the solution, without the usual formation of black precipitate therein, since the bulk of the solution is stored at a tem- Derature below the initiation of thermal decomposition and only the small portion of plating bath held in the plating chamber is heated to d in contact with the catalytic material.

It will be understood that the invention is not limited except as defined by the appended claims.

' We claim:

1. The continuous process of chemically plating with nickel a solid body essentiallvcomprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum. which comprises providing an aqueous solution of a nickel salt and a hypophosphite, wherein the ratio between the nickel ions and the hypophosphite ions insaid solution is within a first predetermined range and the absolute concentration of the hypophosphite ions in said solution is withina second predetermined range and the pH of said solution is within a third predetermined range, storing the bulk of said solution at a relatively low temperature well below the boiling point thereof in a reservoir, holding a small portion of said solution as a bath at a relatively high temperature slightly below the boiling point thereof in a plating chamber, circulating said solution at a low rate from said reservoir to said plating chamher and then back to said reservoir, heating said solution substantially to said relatively high temperature after withdrawal thereof from said 'reservoirand before introduction thereof into said plating chamber, cooling said solution substantially to said relatively low temperature after withdrawal thereof from said plating chamber and before return thereof to said reservoir, immersing said body in said bath in said plating chamber, withdrawing said body from said bath in said plating chamber after a time interval corresponding to the thickness of the nickel plating thereon that'is desired, and adding during said time interval soluble reagents to said solution in said reservoir to maintain in said bath in said plating chamber during said time interval said ratio and said abso ute concentration and access said pH respectively in said first and said second and said third predetermined ranges.

2. The continuous process set forth in claim 1, wherein said solution'is continuously withdrawn .from said reservoir and introduced into the lower portion of said plating chamber and con- ,tinuously withdrawn from the upper portion of said plating chamber and returned to said reservoir.

1 3. The continuous process set forth in claim 1, wherein said solution is continuously circulated ,from said reservoir to said plating chamber and then back to said reservoir, and wherein the volumetric rate of circulation of said solution in cubic feet per minute does not exceed the volume of said bath in cubic feet in said platging chamber.

4. The continuous process of chemically plating with nickel a solid body essentially comprising an element selected from the group consistnickel salt and a hypophosphite and an exaltant,

wherein the ratio between the nickel ions and the .hypophosphite ions in said solution is within a first predetermined range and the absolute concentration of, the hypophosphite ions inv said solution is within a second predetermined range 30,

and the pH of said solution is within a third predetermined range and the absolute concentration of said exaltant in said solution isat least two carboxyl groups for every nickel ion that can be plated out of said solution, storing the bulkof said solution at a relatively low temperature well below the boiling point thereof in areservoir, holding a small portion of said solution as. a bath at a relatively high temperature slightly below the boiling point thereof in a plating chamber, circulating said solution at a low rate from. said reservoir to said plating chamber and then back to said reservoir, heating said solution substantially to said relatively high temperature after withdrawal thereof from said reservoir and before introduction thereof into said plating chamber, cooling said solution substantially to said relatively low temperature after withdrawal thereof from said plating chamber 7 and before return thereof to said reservoir, im-

mersing said, body in, said bath in said plating chamber, withdrawing said body from said bath in saidplating chamber after a time interval corresponding to thethickness of the nickel plating thereon that is desired, and adding during said time interval soluble reagents to said solution in said reservoir to maintain in said bath in said plating chamber during said time interval said ratio and said absolute concentration and said pH respectively in said first and said second and said third predetermined ranges. I 5. The continuous process of chemicallyplating with nickel a solid body essentially comprising an elementselected from the group consist.- ing of iron, cobalt, nickel, aluminum, copper, 65.

silver, gold, palladium and platinum, which comprises providing an aqueous acid solutionof. a nickel salt and a hypophosphite, wherein the ratio between the nickel ions and the hypophosphite ions in said, solution is within a first range 0.25to 0.60 andthe absolute concentration of the hypophosphite ionsexpressed in mole/liter in said solutionis within a second range 0.15. to

V 0.35 and the pH of said solution is within athird range 4.5- to.5.6,-'storing the bulk of said solution at a relatively low "temperature well belowtht i boiling point thereof in a reservoir, holding a small portion of said solution as a bath at a relatively high temperature slightly below the boiling point thereof in a plating chamber, circulating said solution at a low rate from said reservoir to said plating chamber and then back to said reservoir, heating said solution substantially to said relatively high temperature after withdrawal thereof from said reservoir and before introduction thereof into said plating chamber, cooling said solution substantially to said low temperature after withdrawal thereof from said plating chamber and before return thereof to said reservoir, immersing said body in said bath in said plating chamber, withdrawing said body from said bath in said plating chamber after a time interval corresponding to the thickness of the nickel plating thereon that is desired, and adding during said time interval soluble reagents to said solution in said reservoir to maintain in chain saturated aliphatic dicarboxylic acid additive, wherein the ratio between the nickel ions and the hypophosphite ions in said solution is within a first range 0.25 to 1.60 and the absolute concentration of the hypophosphite ions expressed in mole-liter in said solution is within a second range 0.15 to 1.20 and the absolute ion concentration of the additive in said solution is at least two carboxyl groups for every nickel ion that can be plated out of said solution and the pH of said solution is within a third range 4.3 to 6.8, storing the bulk of said solution at a relatively low temperature well below the boiling point thereof in a reservoir, holding a small portion of said solution as a bath at a relatively high temperature slightly below the boiling point thereof in a plating chamber, circulating said solution at a low rate from said reservoir to said plating chamber and then back to said reservoir, heating said solution substantially to said relatively high temperature after withdrawal thereof from said reservoir and before introduction thereof into said plating chamber, coolin said solution substantially to said relatively low temperature after withdrawal thereof from said plating chamber and before return thereof of said reservoir, immersing said body in said bath in said plating chamber, withdrawing said body from said bath in said plating chamber after a time interval corresponding to the thickness of the nickel plating thereon that is desired, and adding during said time interval soluble reagents to said solution in said reservoir to maintain in said bath in said plating chamber during said time interval said ratio and said absolute concentration and said pH respectively in said first and said second and said third ranges.

7. The continuous process of chemically plating with nickel a solid body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises providing an aqueous solution of a nickel salt and a hypophosphite, wherein the ratio between the nickel ions and the .hypophosphite ions in said solution is within a first predetermined range and the absolute concentration of the hypophosphite ions in said solution is within a second predetermined range and the pH of said solution is within a third predetermined range, storing the bulk of said solution at a relatively low temperature well below the boiling point thereof in a reservoir, holding a small portion of said solution as a bath at a relatively high temperature slightly below the boiling point thereof in a plating chamber, circulating said solution at a low rate from said reservoir to said plating chamber and then back to said reservoir, heating said solution substantially to said relatively high temperature after withdrawal thereof from said reservoir and before introduction thereof into said plating chamber, cooling said solution substantially to said relatively low temperature after withdrawal thereof from said plating chamber and before return thereof to said reservoir, immersing said body in said bath in said plating chamber, withdrawing said body from said bath in said plating chamber after a time interval corresponding to the thickness of the nickel plating thereon that is desired, adding during said time interval soluble nickel-containing and hypophosphite-containing reagents to said solution in said reservoir to maintain in said bath in said ple ting chamber during said time interval said ratio and said absolute concentration respectively in said first/ and said second predetermined ranges, and also adding during said time interval a soluble weak alkali to said solution in said reservoir to maintain in said bath in said plating chamber during said time interval said pH within said third predetermined range.

8. The continuous process of chemically plating with nickel a solid body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises providing an aqueous solution of a nickel salt and a hypophosphite and having a predetermined composition, storing the bulk of said solution at a relatively low temperature well below the boiling point thereof in a reservoir, holding a small portion of said solution as a bath at a relatively high temperature slightly below the boiling point thereof in a plating chamber, circulating said solution from said reservoir to said plating chamber and then back to said reservoir, heating said solution substantially to said relatively high temperature after withdrawal thereof from said reservoir and before introduction thereof into said plating chamber, cooling said solution substantially to said relatively low temperature after withdrawal thereof from said plating chamber and before return thereof to said reservoir, im-

mersing said body in said bath in said plating chamber, withdrawing said body from said bath in said plating chamber after a time interval corresponding to the thickness of the nickel plating thereon that is desired, and maintaining substantially said predetermined composition of said bath during said time interval by regenerating said solution during said time interval in said reservoir to compensate for the ingredients of said bath that are exhausted during said time interval in said plating chamber, said regeneration of said solution during said time interval in said reservoir consisting essentially of adding thereto appropriate amounts of soluble nickelcontaining and hypophosphite-containing reagents,

9. The continuous process set forth in claim 1, wherein said soluble reagents added during said time interval to said solution in said reservoir essentially comprise a nickel salt, an alkaline hypophosphite and a weak alkali.

10. The continuous process of chemically plating with nickel a solid body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises providing an aqueous solution of a nickel salt and a hypophosphite and having a predetermined composition, circulating said solution from a reservoir to a plating chamber and then back to said reservoir, heating said solution to a relatively high temperature slightly below the boiling point thereof after withdrawal thereof from said reservoir and before introduction thereof into said plating chamber, cooling said solution to a relatively low temperature well below the boiling point thereof after withdrawal thereof from said plating chamber and before return thereof to said reservoir, immersing said body in the hot portion of said solution in said plating chamber to effect nickel plating on the surface of said body, withdrawing said body from said hot portion of said solution in said plating chamber after a time interval corresponding to the thickness of the nickel plating on the surface of said body that is desired, and

maintaining substantially said predetermined composition of said hot portion of said solution during said time interval in said plating chamber by regenerating the cool portion of said solution during said time interval in said reservoir to compensate for the ingredients of said solution that are exhausted during said time interval in said hot portion or" said solution in said plating chamber, said regeneration of said cool portion of said solution in said reservoir consisting essentially of adding thereto appropriate amounts of soluble nickel-containing and hypophosphitecontaining reagents.

11. The process set forth in claim 10, wherein said relatively high temperature is above C. and said relatively low temperature is substantially below 80 C.

PAUL TALMEY. WILLIAM J. CREHAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,587,110 Fisher June 1, 1926 1,740,979 Golrick Dec. 24, 1929 1,967,856 Beckman July 24, 1934 2,265,467 Alexander et al Dec. 9, 1941 2,430,581 Pessel Nov. 11, 1947 2,532,283 Brenner et al. Dec.5, 1950 

1. THE CONTINUOUS PROCESS OF CHEMICALLY PLATING WITH NICKEL A SOLID BODY ESSENTIALLY COMPRISING AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF IRON, COBALT, NICKEL, ALUMINUM, COPPER, SILVER, GOLD, PALLADIUM AND PLATINU, WHICH COMPRISES PROVIDING AN AQUEOUS SOLUTION OF A NICKEL SALT AND A HYPOPHOSPHITE, WHEREIN THE RATIO BETWEEN THE NICKEL IONS AND THE HYPOPHOSPHITE IONS IN SAID SOLUTION IS WITHIN A FIRST PREDETERMINED RANGE AND THE ABSOLUTE CONCENTRATION OF THE HYPOPHOSPHITE IONS IN SAID SOLUTION IS WITHIN A SECOND PREDETERMINED RANGE AND THE PH OF SAID SOLUTION IS WITHIN A THIRD PREDETERMINED RANGE, STORING THE BULK OF SAID SOLUTION AT A RELATIVELY LOW TEMPERATURE WELL BELOW THE BOILING POINT THEREOF IN A RESERVOIR, HOLDING A SMALL PORTION OF SAID SOLUTION AS A BATH AT A RELATIVELY HIGH TEMPERATURE SLIGHTLY BELOW THE BOILING POINT THEREOF IN A PLATING CHAMBER, CIRCULATING SAID SOLUTION AT A LOW RATE FROM SAID RESERVOIR TO SAID PLATING CHAMBER AND THEN BACK TO SAID RESERVOIR, HEATING SAID SOLUTION SUBSTANTIALLY TO SAID RELATIVELY HIGH TEMPERATURE AFTER WITHDRAWAL THEREOF FROM INTO RESERVOIR AND BEFORE INTRODUCTION THEREOF INTO SAID PLATING CHAMBER, COOLING SAID SOLUTION SUBSTANTIALLY TO SAID RELATIVELY LOW TEMPERATURE AFTER WITHDRAWAL THEREOF FROM SAID PLATING CHAMBER AND BEFORE RETURN THEREOF TO SAID RESERVOIR, IMMERSING SAID BODY IN SAID BATH IN SAID PLATING CHAMBER, WITHDRAWING SAID BODY FROM SAID BATH IN SAID PLATING CHAMBER AFTER A TIME INTERVAL CORRESPONDING TO THE THICKNESS OF THE NICKEL PLATING THEREON THAT IS DESIRED, AND ADDING DURING SAID TIME INTERVAL SOLUBLE REAGENTS TO SAID SOLUTION IN SAID RESERVOIR TO MAINTAIN IN SAID BATH IN SAID PLATING CHAMBER DURING SAID TIME INTERVAL SAID RATIO AND SAID ABSOLUTE CONCENTRATION AND SAID PH RESPECTIVELY IN SAID FIRST AND SAID SECOND AND SAID THIRD PREDETERMINED RANGES. 